Compositions for topical application comprising a peroxide and retinoid

ABSTRACT

The invention relates to a composition for topical application comprising as an active ingredient a peroxide and a retinoid wherein one of said peroxide and retinoid is in the form of first microparticles comprising a solid particulate matter of the active ingredient coated by a metal oxide layer and the other of said peroxide and retinoid is present in an uncoated free form or in a coated form of the active ingredient. The invention further relates to method for treating a surface condition in a subject using said composition, a method for preparing a composition exhibiting improved stability, and a kit comprising: (a) a first composition comprising a peroxide as a first active ingredient; and (b) a second composition comprising a retinoid as a second active ingredient; at least one of said first and said second active ingredient being coated by a metal oxide layer.

FIELD OF THE INVENTION

This invention relates to compositions for topical application.

BACKGROUND OF THE INVENTION

Two of the most commonly used ingredients in topical treatments areBenzoyl Peroxide (BPO) and all trans Retinoic acid (Tretinoin (ATRA))which can be very effective in treating mild to moderate cases ofnon-inflammatory acne. Benzoyl peroxide acts by destroying P. acnes, thebacteria that causes the condition acne. It acts as an antiseptic and asan oxidizing agent, reducing the number of comedones, or blocked pores.Tretinoin (ATRA) is a unique topical medication used in the treatment ofacne that allows the keratin plugs of microcomedones to be expelled,thus fewer lesions are able to rupture and cause papules, pustules andnodules of inflammatory acne. A combination drug of BPO and ATRA shouldhave both comedogenesis and bacteriostatic effect in acne treatment.However, two main obstacles to such combination is instability of ATRAin presence of BPO and severe adverse events such as erythema,irritation, burning, stinging, scaling and itching.

Compositions and methods for treatment acne comprising BPO and/or aRetinoid are described for example in U.S. Pat. No. 4,350,681, U.S. Pat.No. 4,361,584, U.S. Pat. No. 4,387,107, U.S. Pat. No. 4,497,794, U.S.Pat. No. 4,671,956, U.S. Pat. No. 4,960,772, U.S. Pat. Nos. 5,086,075,5,145,675, U.S. Pat. No. 5,466,446, U.S. Pat. No. 5,632,996, U.S. Pat.No. 5,767,098, U.S. Pat. No. 5,851,538, U.S. Pat. Nos. 5,955,109,5,879,716, 5,955,109 U.S. Pat. No. 5,998,392, U.S. Pat. No. 6,013,637,U.S. Pat. No. 6,117,843, Pub. No.: US 2003/0170196, US2002064541, and20050037087. H. Tatapudy et al., Indian Drugs, 32(6), 239-248, 1995,describes benzoyl peroxide microcapsules, prepared by coacervation phaseseparation process.

Sol-Gel process has been used to encapsulate various active ingredients,thus isolating the active ingredient from the environments.

U.S. Pat. Nos. 6,303,149, 6,238,650, 6,468,509, 6,436,375, US2005037087,US2002064541, and International publication Nos. WO 00/09652,WO00/72806, WO 01/80823, WO 03/03497, WO 03/039510, WO00/71084,WO05/009604, and WO04/81222, disclose sol-gel microcapsules and methodsfor their preparation. EP 0 934 773 and U.S. Pat. No. 6,337,089 teachmicrocapsules containing core material and a capsule wall made oforganopolysiloxane, and their production. EP 0 941 761 and U.S. Pat. No.6,251,313 also teach the preparation of microcapsules having shell wallsof organopolysiloxane. U.S. Pat. No. 4,931,362 describes a method offorming microcapsules or micromatrix bodies having an interiorwater-immiscible liquid phase containing an active, water-immiscibleingredient. Microcapsules prepared by a sol-gel process are alsodisclosed in GB2416524, U.S. Pat. No. 6,855,335, WO03/066209.

There still is a widely recognized need for a composition comprising BPOand retinoid in which the active ingredients are chemically stable whenformulated together in the same composition.

SUMMARY OF THE INVENTION

The present invention relates to a composition for topical applicationcomprising as an active ingredient a peroxide and a retinoid wherein oneof said peroxide and retinoid is in the form of first microparticlescomprising a solid particulate matter of the active ingredient coated bya metal oxide layer and the other of said peroxide and retinoid ispresent in an uncoated free form or in a coated form of the activeingredient.

The present invention additionally relates to a composition for topicalapplication comprising as an active ingredient benzoyl peroxide and alltrans retinoic acid wherein one of said benzoyl peroxide and all transretinoic acid is in the form of first microparticles comprising a solidparticulate matter of the active ingredient coated by a metal oxidelayer and the other of said benzoyl peroxide and all trans retinoic acidis present in an uncoated free form or in a coated form of the activeingredient.

The present invention further relates to a composition for topicalapplication comprising as an active ingredient benzoyl peroxide andtazarotene wherein one of said benzoyl peroxide and tazarotene is in theform of first microparticles comprising a solid particulate matter ofthe active ingredient coated by a metal oxide layer and the other ofsaid benzoyl peroxide and tazarotene is present in an uncoated free formor in a coated form of the active ingredient.

The present invention further relates to a composition for topicalapplication as defined in the present invention said composition havingreduced side affects as compared to a reference composition, in whichthe active ingredients are not coated.

The present invention further relates to a method for treating a surfacecondition in a subject comprising topically administering onto thesurface a composition as described in the present invention.

The present invention additionally relates to a method for preparing acomposition comprising as active ingredients a peroxide and a retinoidwhich are chemically unstable when formulated together, wherein thecomposition exhibits improved stability of at least one of the activeingredients, the method comprising:

(a) separating said peroxide and retinoid from each other in thecomposition by coating a solid particulate matter of one of said activeingredients by a metal oxide coating layer to form first microparticles,the other of said peroxide and retinoid is incorporated into thecomposition in an uncoated free form or in a coated form of the activeingredient; and

(b) adding excipients for the preparation of the composition.

Further the present invention relates to a kit comprising: (a) a firstcomposition comprising a peroxide as a first active ingredient; and (b)a second composition comprising a retinoid as a second activeingredient; at least one of said first and said second active ingredientbeing coated by a metal oxide layer.

Moreover the present invention relates to a method of using the kit asdescribed in the present invention wherein said first composition andsaid second composition are applied concomitantly or sequentially onto asurface of a subject's body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the irritation test results performed according toExample 6.

FIG. 2: shows the influence of BHT on the stability of free tretinoincrystals with BPO.

FIG. 3: shows the stability results for tretinoin encapsulated by 10cycles, under assorted conditions.

FIG. 4: shows the influence of the number of coating cycles on thestability of the encapsulated tretinoin.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the findings that it is possible toformulate two or more reactive active agents in the same composition.Surprisingly it was found in the present invention that it is possibleto formulate a peroxide (preferably benzoyl peroxide) and a retinoid(preferably retinoic acid) which are chemically reactive, in the samecomposition by coating a solid particulate matter of one of these activeagents (or each of these active agents) by a metal oxide coating, thusseparating these two active agents from each other in the samecomposition. Such a composition was found to be advantageous withrespect to the chemical stability of the active ingredients and furtherfound to have reduced side effects as compared to a referencecomposition comprising the uncoated active agents.

Thus, the present invention relates to a composition for topicalapplication comprising as an active ingredient a peroxide and a retinoidwherein one of said peroxide and retinoid is in the form of firstmicroparticles comprising a solid particulate matter of the activeingredient coated by a metal oxide layer and the other of said peroxideand retinoid is present in an uncoated free form or in a coated form ofthe active ingredient.

As used herein unless otherwise indicated the term “microparticles”refers particles having a core shell structure. It is appreciated thatsome of the microparticles may at times be formed from two or more coreparticles of a solid water insoluble particulate matter and mayaccordingly include, at times, more than one core, such cores beingseparated from each other by a metal oxide region.

The size of the microparticles (denoted herein also by the general term“particles”) as will be referred to herein refers to D₉₀ meaning that90% of the particles have the stated dimension or less (measured byvolume). Thus, for examples, for spherical particles stated to have adiameter of 10 micrometer (“microns”), this means that the particleshave a D₉₀ of 10 microns. The D₉₀ (termed also d(0.9)) may be measuredby laser diffraction. For particles having a shape other than spheres,the D₉₀ refers to the mean average of the diameter of a plurality ofparticles.

The core (i.e. solid particulate matter) may be of any shape for examplerod-like, plate-like, ellipsoidal, cubic, or spherical shape.

In the case of cores having a spherical shape, the diameter (D₉₀) may bein the range of 0.3 to 90 microns, preferably 0.3 to 50 microns, morepreferably 1 to 50, even more preferably 5 to 30 microns.

By the term “the diameter (D90) may be in the range of 0.3 to 90microns” is meant that 90% by volume of the particles (in this case theparticle's core) may be less than or equal to a value in the range of0.3 to 90 microns.

For generally cubic-shaped cores or cores having a shape resembling thatof a cube, the mean size of a side may be in the range 0.3 to 80microns, preferably 0.3 to 40 microns, more preferably 0.8 to 40, evenmore preferably 4 to 15 microns.

For rod-like shaped, ellipsoidal-shaped and plate-like shaped cores, thelargest dimension (that of the longest axis) is typically in the range10 to 100 microns, preferably 15 to 50 microns; and the smallestdimension is typically in the range 0.5 to 20 microns and morepreferably 2 to 10 microns.

According to a preferred embodiment of the present invention, themicroparticles (coated particulate matter) have a diameter (d90) of 0.5to 100 μm or preferably the diameter of the microparticles is in therange of 1 to 50 μm and most preferably in the range of 5 to 30 μm. Itis appreciated that the microparticles of the present invention arecomposed of distinct regions of the metal oxide layer in the corematerial (i.e. the water insoluble particulate matter).

Further according to a preferred embodiment of the present invention theobtained metal oxide coating layer has a width (thickness) of 0.1 micronor above, preferably 0.1-10 micron.

Additionally according to a preferred embodiment of the presentinvention the obtained metal oxide coating layer has a width (thickness)of 0.3 micron or above, preferably 0.3-10 micron.

Additionally according to a preferred embodiment of the presentinvention, the thickness of said metal oxide layer is in the range0.1-10 micron. More preferably 0.1-3 micron, and even more preferably0.1-1 micron. The thickness of the metal oxide layer may also bepreferably in the range 0.3 to 3 micron, and most preferably 0.3 to 2micron.

Further according to a preferred embodiment of the present invention theobtained metal oxide coating layer has a width (thickness) of about 0.1,0.2, 0.3, 0.5, 0.7, 1, 1.5, 2 or 5 micron or above, preferably up to 10micron.

The width of the metal oxide layer may be determined for example by aTransmission Electron Microscope or Confocal Microscope such that in acircular cross sectional area of the particle the smallest width is atleast e.g. 0.1 micron (the width is determined as the smallest distancefrom the surface of the particle (i.e. metal oxide surface) to thecore-metal oxide interface).

The microparticles are preferably characterized in that the corematerial is substantially free of the metal oxide and further in thatthe metal oxide layer is substantially free of said core material, e.g.either as particle dispersion (in the nano-metric range of below 0.1 μm)of the particulate matter or as molecular dispersion of said particulatematter.

Thus, according to a preferred embodiment of the present invention, themetal oxide layer is substantially free of core material (either in theform of molecules or as nano-metric particles). The term “substantiallyfree” in this context denotes that the concentration of the molecules ofthe core material or the concentration of the nano-metric particles ofthe core material is negligible as compared to the metal oxide.Similarly, by the term “the core material is substantially free of themetal oxide” is meant that the concentration of the metal oxide in thecore is negligible as compared to the core material. The microparticles(i.e. first microparticles) are preferably non leaching when dispersedin a carrier and most preferably non leaching in an aqueous basedcarrier.

According to another embodiment when the microparticles are prepared bya method such as spray drying, the core material comprising the activeagent may further comprise up to about 30% w/w, preferably up to about20% metal oxide and the metal oxide coating layer may further compriseup to about 30% w/w, preferably up to about 20% w/w of the active agent.

By the term “non-leaching” it is meant that the leaching of theparticulate matter (active agent) from the particles into anaqueous-based liquid is less than 5% w/w, preferably less than 3%, morepreferably less than 1% w/w even more preferably less than 0.5% w/w, andmost preferably less than 0.1% w/w at room temperature (20° C.), undergentle agitation for 1 hour or until a steady state concentration isachieved. Typically, the aqueous-based liquid is water. The valuesindicated above refer to the percentage of the active agent leached intoan aqueous medium relative to the initial amount of the active agent inthe particles. The leaching values indicated above refer preferably to adispersion having a concentration of the particulate matter in theaqueous medium higher than 0.1% w/w, more preferably higher than 1% w/w,even more preferably higher than 3% w/w, and most preferably higher than10% w/w. For retinoid the leaching values indicated above referpreferably to a dispersion having a concentration of the particulatematter in the aqueous medium higher than 0.01% w/w.

According to a preferred embodiment of the present invention the weightratio of said metal oxide to said solid particulate matter is in therange of 1:99 to 50:50. The weight ratio of the metal oxide layer to thesolid particulate matter may be also in the range of 3:97 to 50:50, 5:95to 50:50, 10:90 to 50:50, 5:95 to 30:70, 10:90 to 30:70. Further,according to a preferred embodiment of the present invention the rateratio of the metal oxide to the solid particulate matter is in the rangeof 10:90 to 20:80.

According to another preferred embodiment of the present invention, whenspray drying method is used, the weight ratio of the metal oxide to saidsolid particulate matter may be in the range 5:95 to 95:5.

As used herein by the term “uncounted free form” is meant that theactive ingredient (peroxide or retenoid) is present in the compositionin its “naked” form meaning that it is not intimately embedded,encapsulated, entrapped or encased in a polymeric carrier, and ispresent in the composition in direct contact with the compositioncarrier. As used herein by the term “coated form of the activeingredient” is meant that the active ingredient is embedded, dispersed,entrapped, or encased, e.g. as a solid dispersion or moleculardispersion in a polymeric carrier which may be an organic or inorganiccarrier and which may serve as a matrix for dispersing the activeingredient or as encapsulated material coating said active ingredient(i.e the active ingredient is present in a core or is a core materialencapsulated by a shell composed of a polymeric material which may be anorganic or inorganic polymer).

According to a more preferred embodiment of the present invention, saidcoated form of the active ingredient is second microparticles comprisinga solid particulate matter of the active ingredient coated by a metaloxide layer.

Further, according to a preferred embodiment of the present invention,said first microparticles comprise a solid particulate matter of aperoxide coated by a metal oxide layer.

According to a more preferred embodiment of the present invention, saidperoxide is in the form of first microparticles comprising solidparticulate matter of peroxide coated by a metal oxide layer and saidretinoid is in the form of second microparticles comprising a solidparticulate matter of the retinoid coated by a metal oxide layer.

The metal oxide coating layer is highly advantageous since it is capableof isolating the particulate matter of the active agent from itssurrounding medium, thus preventing cross-reactivity of the activeagents present in the same composition and yet enables the release theparticulate matter upon application to the surface to be treated.

According to a preferred embodiment of the present invention, the coatedform of the active ingredient may be in form of a polymeric microspongewhere the active ingredient is adsorbed or entrapped in said microspongeas described for example in U.S. Pat. Nos. 4,690,825; 5,145,675,5,879,716 and 5,955,109, incorporate herein by reference in theirentirety.

As used herein the term “peroxide” refers to a solid water insolubleagent including a peroxide moiety.

The term “solid water insoluble agent” refers to a solid material havingsolubility in water of less than 3% w/w, typically less than 1% and attimes less than 0.5% w/w at room temperature (20° C.). The “solid waterinsoluble agent” may have a solubility of less than 0.1% w/w.

The “solid water insoluble agent” may also be termed herein as “solidwater insoluble particulate matter” or “solid particulate matter”.

According to a preferred embodiment of the present invention, theperoxide is benzoyl peroxide.

Additionally, according to a preferred embodiment of the presentinvention the retinoid is selected from all trans retinoic acid(tretinoin), iso-tretinoin, adapalene, tazarotene, and mixtures thereof.

Thus, the present invention further relates to a composition for topicalapplication comprising as an active ingredient benzoyl peroxide and alltrans retinoic acid wherein one of said benzoyl peroxide and all transretinoic acid is in the form of first microparticles comprising a solidparticulate matter of the active ingredient coated by a metal oxidelayer and the other of said benzoyl peroxide and all trans retinoic acidis present in an uncoated free form or in a coated form of the activeingredient.

The composition of the present invention comprises a carrier. Accordingto a preferred embodiment of the present invention the carrier is in theform of a ointment, a cream, a lotion, an oil, a solution (preferably anaqueous solution), an emulsion, a gel, a paste, a milk, an aerosol, apowder, or a foam. Preferably the carrier is an aqueous-based carrier(such as a gel, oil-in water emulsion or oil-in water cream, aqueoussolution, foam, lotion, spray).

Thus, the final form of the composition may be any of the above forms,mentioned with respect to the carrier, where the microparticles aredispersed in the carrier. The final form of the composition may also bein the form of a wash or cleanser.

Moreover, according to a preferred embodiment of the present invention,the composition having an improved stability as compared to a referencecomposition the difference between said composition and the referencecomposition being in that the reference composition and the activeingredients are not coated.

As used herein by the term “improved stability” is meant that thedegradation of the retinoid (e.g. tretinoin) in the presence of theperoxide (e.g. benzoyl peroxide) is preferably less than 30%, morepreferably less than 20%, even more preferably less than 10% of theinitial retinoid concentration in a time range of 3 month at roomtemperature (20-25° C.), or 1 month at 30° C. Even more preferablydegradation of the retinoid (e.g. tritenoin) in the presence of theperoxide (e.g. benzoyl peroxide) is less than 30%, more preferably lessthan 20%, even more preferably less than 10% of the initial retinoidconcentration in the time range of 1 year at room temperature (20-25°C.), or 3 months at 30° C. or 1.5 months at 40° C., and most preferably,degradation of the retinoid (e.g. tritenoin) in the presence of theperoxide (e.g. benzoyl peroxide) is less than 30%, more preferably lessthan 20%, even more preferably less than 10% of the initial retinoidconcentration in the time range of 2 years at room temperature (20-25°C.), or 6 months at 30° C. or 3 months at 40° C. Additionally, accordingto a preferred embodiment of the present invention, the compositionhaving improved efficacy over individual active ingredients. Theindividual active ingredients may be in an uncoated free form or in acoated form of the active ingredient as described in the presentinvention.

According to a preferred embodiment of the present invention thecomposition further comprising an additional active agent.

Preferably the additional active agent is an antibiotic agent. Morepreferably the antibiotic agent is an antibiotic of the lincomycinfamily. Most preferably the antibiotic of the lincomycin family isclindamycin, a pharmaceutical acceptable salt thereof, or an esterthereof.

The antibiotic may be present in an uncoated free form or in a coatedform of the active ingredient. The uncoated free form and coated freeform may be as described in the present invention with respect to theperoxide and retinoid.

According to a preferred embodiment of the present invention, acomposition comprising benzoyl peroxide (BPO), all-trans retinoic acid(ATRA) and an antibiotic as described in the present invention hasimproved efficacy over at least one of the following combinations: BPOand ATRA, BPO and antibiotics, ATRA and antibiotics.

Preferably, the metal oxide is selected from silica, titania, alumina,zirconia, ZnO, and mixtures thereof. Most preferably the metal oxide issilica.

Moreover according to a preferred embodiment of the present invention,the microparticles (coated particulate matter) have a diameter of0.5-100 micron. Preferably the particles have a diameter of 0.8-100micron, more preferably 1-50 micron and most preferably 2-30 micron.

According to certain embodiments of the present invention, the surfaceof the metal oxide later of the coated particulate matter may bechemically modified by organic groups, preferably hydrophobic groups,attached to its surface.

The hydrophobic groups may be for example an alkyl groups (such alkylgroups may be further substituted with one or more fluoro atoms), arylgroups (such as benzyl or phenyl), and combinations thereof. The groupsmay be as described below with respect to the process.

Further according to a preferred embodiment of the present inventionsaid first microparticles are prepared by deposition of metal oxide onthe surface of the solid particulate matter. The deposition of metaloxide on the surface of the particulate matter may be performed byprecipitation of a metal oxide salt onto the surface of the particulatematter, forming a metal oxide layer thereon as will be described belowor by a spray drying method.

Preferably the first microparticles are prepared by a processcomprising:

(a) contacting the solid, water-insoluble particulate matter, with anionic additive and an aqueous medium to obtain a dispersion of saidparticulate matter having positive charges on its surface;

(b) coating the solid, water-insoluble particulate matter, byprecipitation of a metal oxide salt onto the surface of the particulatematter, forming a metal oxide coating layer thereon; and

(c) aging said coating layer.

Still further according to a preferred embodiment of the presentinvention said first microparticles are prepared by a process forcoating a solid, water-insoluble particulate matter, with a metal oxidecomprising:

(a) contacting the solid, water-insoluble particulate matter with anionic additive and an aqueous medium to obtain a dispersion of saidparticulate matter having positive charges on its surface;

(b) subjecting the particulate matter to a coating procedure comprisingprecipitating a metal oxide salt onto the surface of the particulatematter to form a metal oxide layer thereon thereby to obtain particulatematter coated by a metal oxide coating layer;

(c) repeating step (b) at least 4 more times; and

(d) aging said coating layer.

In the process described the solid, water-insoluble particulate matterrefers to the peroxide or retinoid. The process described may also beused to coat additional active ingredients (e.g. antibiotics) which maybe incorporated into the composition described in the present invention.

Step (a) of the process may further comprise reducing the particle sizeof the particulate matter to the desired particle size for example bymilling, or homogenization.

Preferably step (c) of the process described above is repeated 4 toabout 1000 times. This means that preferably step (b) of the processdescribed above is repeated 4 to about 1000 times.

Preferably the process comprising repeating step (c) 4 to about 300times, and more preferably 4 to about 100 times, Even more preferablystep (c) of the process described above is repeated 5-80 times and mostpreferably 5-50 times. This means that preferably step (b) is repeatedas indicated above with respect to step (c).

By the term “repeated 4 to about 1000 times” is meant that the processmay be repeated 4, 5, 6, 7, 8, 9 . . . etc. times up to and includingabout 1000 times.

According to a preferred embodiment of the present invention step (d)further comprising after aging, separating the coated particulate matterfrom the dispersing aqueous medium, such as by filtration,centrifugation or decantation and optionally rinsing and redispersingthe obtained coated particulate matter in an aqueous medium.

During the coating process it is preferred that at least 50% of thecontent the particulate matter (active agent) in the aqueous medium isin a solid state during the coating process.

According to a preferred embodiment of the present invention the processcomprising:

(a) contacting the solid, water-insoluble particulate matter, with afirst cationic additive and an aqueous medium to obtain a dispersion ofsaid particulate matter having positive charges on its surface;

(b) subjecting the particulate matter to a coating procedure comprisingprecipitating a metal oxide salt onto the surface of the particulatematter to form a metal oxide coating layer on the particulate matter;

(b1) in an aqueous medium contacting the coated particulate matter witha surface adhering additive being one or both of (i) a second cationicadditive, and (ii) a non-ionic additive;

(b2) subjecting the particulate matter obtained in step (b1) to acoating procedure as in step (b);

(c) repeating steps (b1) and (b2) at least 3 more times; and

(d) aging the metal oxide coating layer.

Preferably the process comprising repeating step (c) 3 to about 1000times.

Preferably the process comprising repeating step (c) 3 to about 300times, and more preferably 3 to about 100 times.

As used herein by the term “repeating step (c) 3 to about 1000 times” ismeant that the process may be repeated 3, 4, 5, 6, 7, 8, 9 etc. times upto and including about 1000 times.

Thus, preferably steps (b1) and (b2) are repeated as indicated withrespect to step (c).

Additionally according to a preferred embodiment of the presentinvention the process comprising:

(a) contacting the solid, water-insoluble particulate matter, with ananionic additive, a first cationic additive and an aqueous medium toobtain a dispersion of said particulate matter having positive chargeson its surface;

(b) subjecting the particulate matter to a coating procedure comprisingprecipitating a metal oxide salt onto the surface of the particulatematter to form a metal oxide coating layer on the particulate matter;

(b1) in an aqueous medium contacting the coated particulate matter withone or both of (i) a second cationic additive, and (ii) a non-ionicadditive;

(b2) subjecting the particulate matter obtained in step (b1) to acoating procedure as in step (b);

(c) repeating steps (b1) and (b2) at least 3 more times; and

(d) aging the metal oxide coating layer.

When an anionic additive and first cationic additive are used in step(a) of the process, preferably the anionic additive is added before thefirst cationic additive.

Preferably step (c) is repeated 3 to about 1000 times. Preferably step(c) is repeated 3 to about 300 times, and more preferably 3 to about 100times. This means that preferably steps (b1) and (b2) are repeated asindicted above with respect to step (c).

Step (a) of the process may be conducted for example by (i) contactingthe particles with dry ionic additives and then suspending both in anaqueous medium to obtain a dispersion of said particulate matter havingpositive charges on its surface, or alternatively by (ii) suspending thesolid, water-insoluble particulate matter in an aqueous mediumcomprising ionic additives to obtain a dispersion of said particulatematter having positive charges on its surface.

According to another preferred embodiment of the process may comprise(a) contacting the solid, water-insoluble particulate matter, with anionic additive selected from (i) an anionic additive; (ii) a firstcationic additive, and a combination thereof, and an aqueous medium toobtain a dispersion of said particulate matter having positive chargeson its surface; (b), (b1), (b2), (c), (d) are as described herein.

The concentration of the ionic additives in the dispersion can be about0.001% to about 30%, preferably about 0.01% to about 10% w/w and mostpreferably about 0.1% up to about 5% w/w. The solid content of the waterdispersion can be about 0.1% to about 80% w/w, preferably about 1% toabout 60% w/w most preferably about 3% to about 50% w/w.

The purpose of step (a) is to modify the electrical charge of theparticulate matter by using ionic additives such that it will be madereactive to the attachment of the metal oxide layer.

For preparing the core material of the particles, the particulate matterought to be suitably coated with an ionic additive (e.g. cationicadditive), such that it can be attached to the precipitated metal oxidesalt.

Preferably the ionic additive is selected from a cationic additive, ananionic additive, and a combination thereof. The cationic additive maybe a cationic surfactant and/or cationic polymer. The anionic additivemay be an anionic surfactant and/or anionic polymer.

The particulate matter is contacted with an ionic additive, for exampleby mixing it with a solution of a cationic surfactant and/or cationicpolymer or an anionic surfactant and a cationic additive (e.g. cationicsurfactant and/or cationic polymer). Cationic and anionic surfactantsare particularly effective in being adsorbed upon the surface of theparticulate matter. The ionic additive may also be anionic polymers usedin combination with a cationic additive. The cationic surfactant and/orthe cationic polymer and optionally further the anionic surfactant (oranionic polymer) need to be used in sufficient amount to providepositive charges on the surface of the particulate matter. A monolayerof the ionic additive is preferred, but the coating need not becontinues. It is sufficient that there are at least spots of cationicadditive. These spots will then serve as anchors for the attachment ofthe metal oxide layer. It is preferred that there are fairly uniformdistribution of these anchoring points on the core surface so that asthe metal oxide layer builds up it will bridge over and be firmlyattached to the core.

According to one preferred embodiment said first and said secondcationic additive are the same.

According to another preferred embodiment said first and said secondcationic additive are different.

More preferably the first ionic additive is a an anionic surfactant andthe second ionic additive is a cationic polymer

Most preferably the first cationic additive is a cationic surfactant andthe second cationic additive is a cationic polymer.

According to another preferred embodiment, the first cationic additiveis a cationic surfactant and the additive in step (b1) is a non-ionicadditive (e.g. a non-ionic polymer).

Preferably the coated particulate matter and the second cationicadditive are mixed, and most preferable said mixing is under vigorousstirring (e.g. mixer speed above 1000 rpm).

According to a preferred embodiment of the present invention the processfurther comprising following step (d): (e) separating the coatedparticulate matter from the aqueous medium and optionally rinsing andredispersing the coated particulate matter in an aqueous medium.

Preferably the separation of the coated particulate matter is conductedby a method such as filtration centrifugation, decantation, dialysis, orby evaporation of the aqueous medium.

Additionally according to a preferred embodiment of the presentinvention, step (b) comprises adding a metal oxide salt to the aqueousmedium; and optionally acidifying the aqueous medium.

Further according to a preferred embodiment of the present invention,step (b2) comprises adding a metal oxide salt to the aqueous medium; andoptionally acidifying the aqueous medium.

Preferably step (b1) further comprising adjusting the pH of thedispersion obtained in (b) to a value higher than the isoelectric pointof the metal oxide before adding the second cationic additive, morepreferably to a pH value of at least about 1 unit higher than theisoelectric point of the metal oxide, before adding the second cationicadditive.

Preferably step (b1) further comprising adjusting the pH of thedispersion obtained in (b) to a value higher than the isoelectric pointof the metal oxide before adding one or both of (i) a second cationicadditive, and (ii) a non-ionic additive, more preferably to a pH valueof at least about 1 unit higher than the isoelectric point of the metaloxide, before adding the second cationic additive.

For example, in case the metal oxide is silica (e.g. having anisoelectric point in the range 1.7-2.5) the preferred pH may be at leastin the range of about 2.5-6.5.

The purpose of the pH adjustment of the dispersion to a value higherthan the isoelectric point of the metal oxide is to form negativelycharged metal oxide on the particulate matter surface that will be boundto the positive charges of the second cationic additive thus enablingthe attachment of the second cationic additive to the surface of theparticulate matter.

The non-ionic additive is of a kind that adheres to the surface(“surface-adherent”). An example is a non-ionic polymer. The non-ionicadditive may be used alone or in addition to the second cationicsurfactant.

Preferably the particulate matter/metal oxide salt weight ratio, in eachof the steps (b) or (b2) is about 5,000/1 to about 20/1, preferablyabout 5,000/1 to about 30/1, or about 5,000/1 to about 40/1, morepreferably about 1,000/1 to about 40/1, and most preferably about 500/1to about 80/1.

Preferably the particulate matter/cationic additive weight ratio, instep (b1) is about 25,000/1 to about 50/1, preferably about 5,000/1 toabout 100/1, and most preferably about 2000/1 to about 200/1.

According to preferred embodiment the particulate matter/metal oxidesalt weight ratio, in each of the steps (b) or (b2) is about 5,000/1 toabout 65/1, and more preferably about 1000/1 to about 100/1.

Preferably the particulate matter/cationic additive weight ratio, instep (b1) is about 10,000/1 to about 100/1, and more preferably about5000/1 to about 200/1.

In case a non-ionic additive (e.g. non-ionic polymer) is used alone orin addition to the second cationic additive, the weight ratios of the ofthe first coated particulate matter to the (i) non-ionic additive or(ii) a combination of a non-ionic additive and second cationic additive,and the weight ratios of the further processed coated particulate matterto the (i) non-ionic additive or (ii) the combination of the non-ionicadditive and second cationic additive, may be as indicated above withrespect to the second cationic additive.

The aging in step (d) is crucial for obtaining a strengthened and denselayer of metal oxide.

According to a preferred embodiment of the present invention step (d)comprises raising the pH to a value in the range 3-9, preferably to arange of 5-7, and mixing, e.g. by stirring, the suspension (dispersion)in this pH range for a period of e.g. at least 2 h (two hours).Preferably stirring is for 2-96 h, more specifically 2-72 h, morepreferably at least 10 h (for example 10-72 h). The stirring ispreferably a gentle stirring, preferably in the range 200-500 rpm.

Upon completion of aging, the separation (e.g filtration, centrifugationor decantation) will be easy to perform (due to the hard metal oxidelayer formed) and the obtained cake or concentrated dispersion will beeasily redispersed in an aqueous medium to form a dispersion ofparticles.

The purpose of aging in step (d) is to obtain a strengthened and denserlayer of metal oxide.

In the absence of the aging step a thinner and softer layer of metaloxide would be obtained since the metal oxide salt upon precipitationforms a gel layer of metal oxide which may disintegrate or erode uponseparation and washing or by mechanical stirring.

The aging may be conducted at a temp of 4-90° C., preferably at 15-60°C. and most preferably the aging is conducted at a temperature 20°C.-40° C.

Thus the repeated steps of coating and aging at the end of the processalso enable the growth of thicker and stronger layer of metal oxide.Most preferably aging is not conducted between the repeated coatingsteps (i.e between the repeated coating step (b)), but only at the endof the process. Thus most preferably the aging is conducted only at theend of the process described herein.

Preferably the metal oxide is selected from Silica, Titania, Alumina,Zirconia, ZnO, and mixtures thereof. Most preferably the metal oxide issilica.

The metal oxide salt is preferably an alkali metal oxide salt, e.g.sodium or potassium salt.

According to a preferred embodiment of the present invention the metaloxide salt is selected from sodium silicate, potassium silicate, sodiumaluminate, potassium aluminate, sodium titanate, potassium titanate,sodium zirconate, potassium zirconate, and mixtures thereof. Mostpreferably the metal oxide salt is a silicate salt.

According to certain embodiments, the process may further compriseadding a colloidal metal oxide suspension, preferably aqueous-basedsuspension (comprising nanometric metal oxide (nanoparticles of metaloxide)) during the coating procedure. Preferably the colloidal metaloxide suspension is selected from colloidal silica suspension, colloidaltitania suspension, colloidal alumina suspension, colloidal zirconiasuspension, colloidal ZnO suspension, and mixtures thereof. Thecolloidal metal oxide suspension may be added during the coating process(e.g. in step (b) in one or more of its repeated steps). Preferably thesize of the nanometric metal oxide in diameter is in the range between5-100 nm (average particle size diameter). The weight ratio of thenanometric metal oxide to the metal oxide salt may be in the range 95:5to 1:99 preferably 80:20 to 5:95 more preferably 70:30 to 10:90, mostpreferably about 60:40 to 20:80. The weight ratio of the nanometricmetal oxide to the metal oxide salt may be about 50:50.

According to other embodiments, the process does not include addition ofcolloidal metal oxide suspension during the coating process. Accordingto this embodiment nanometric metal oxide particles (nanoparticles ofmetal oxide) are not added during the coating process.

Further according to a preferred embodiment of the present invention theionic additive is selected from a cationic surfactant, anionicsurfactant, a cationic polymer, and mixtures thereof. When an anionicsurfactant is used, preferably a cationic additive is further added suchas a cationic surfactant and/or a cationic polymer.

Preferably the cationic additive is selected from a cationic surfactant,a cationic polymer, and mixtures thereof.

According to a preferred embodiment the first cationic additive is acationic surfactant, and the second cationic additive is a cationicpolymer.

The first cationic additive is preferably a cationic surfactant.

Preferably the cationic surfactant selected from monoalkylquaternaryammonium salts, dialkyl quaternary ammonium salts, and mixtures thereof.

Preferably the monoalkylquaternary ammonium salts are selected frombenzethonium chloride, benzalkonium chloride, cetyltrimethylammoniumchloride (CTAC), cetyltrimethylammonium bromide (CTAB),lauryltrimethylammonium chloride, stearyltrimethylammonium chloride,cetylpyridinium chloride, and mixtures thereof.

Most preferably the monoalkylquaternary ammonium salt iscetyltrimethylammonium chloride.

Preferably the dialkyl quaternary ammonium compound isdistearyldimethylammonium chloride.

Additional cationic surfactants which can be used are described in: JohnA. Wenninger et al. (Editors) International Cosmetic IngredientDictionary and Handbook (Eighth Edition 2000), Vol. 2 pp. 1140-1147,Published by The cosmetic, Toiletry, and Fragnance Association,incorporated herein by reference in its entirety.

The ionic additive may be an anionic surfactant.

Preferably the anionic surfactant is selected from alkyl benzenesulphonic acids and salts, alkyl ether carboxylic acids and salts, alkylsulphosuccinamates, alkyl sulphossucinates, alpha olefin sulphonates,aromatic hydrocarbon sulphonic acids and salts, fatty alcohol ethoxysulphates, fatty alcohol sulphates, phosphate esters and mixturesthereof.

Preferably the alkyl benzene sulphonic acid salt is sodium dodecylbenzene sulphonate, the fatty alcohol sulphate is sodium laurylsulphate, the alkyl sulphossucinates is sodium dioctyl sulphossucinate,and mixtures thereof.

Additional anionic surfactants which can be used are described in: JohnA. Wenninger et al. (Editors) International Cosmetic IngredientDictionary and Handbook (Eighth Edition 2000), Vol. 2 pp. 1140-1147,Published by The cosmetic, Toiletry, and Fragnance Association,incorporated herein by reference in its entirety.

Preferably the weight ratio of the ionic additive to the water-insolubleparticulate matter is in the range 1:1000-1:10, more preferably in therange 1:200-1:50, most preferably about 1:100. The ratios indicatedabove refer to an ionic additive such as the first cationic additive orto the combination of a first cationic additive and an anionic additive.

The second cationic additive may be a cationic polymer, a cationicsurfactant or mixtures thereof. The cationic surfactant may be asdescribed above.

According to a preferred embodiment of the present invention the secondcationic additive is a cationic polymer.

Preferably the weight ratio of the first coated particulate matter (i.e.in step (b1)) to the second cationic additive is in the range of about25,000/1 to about 50/1, more preferably about 5,000/1 to about 100/1most preferably about 2000/1 to about 200/1.

Preferably the weight ratio of the further processed coated particulatematter (e.g. in the repeated steps described in step (c)) to the secondcationic additive is in the range of about 25,000/1 to about 50/1, morepreferably about 5,000/1 to about 100/1, most preferably about 2000/1 toabout 200/1.

Preferably the particulate matter/cationic additive weight ratio, instep (b1) is about 10,000/1 to about 100/1, and more preferably about5000/1 to about 200/1.

Preferably the weight ratio of the further processed coated particulatematter (e.g. in the repeated steps described in step (c)) to the secondcationic additive is in the range of about 10,000/1 to about 100/1, andmore preferably about 5000/1 to about 200/1.

In case a non-ionic additive (e.g. non-ionic polymer) is used alone orin addition to the second cationic additive, the weight ratios of the ofthe first coated particulate matter to the (i) non-ionic additive or(ii) a combination of a non-ionic additive and second cationic additive,and the weight ratios of the further processed coated particulate matterto the (i) non-ionic additive or (ii) the combination of the non-ionicadditive and second cationic additive, may be as indicated above withrespect to the second cationic additive.

Preferably the cationic polymer (of the first cationic additive orsecond cationic additive) is selected from poly(ethyleneimine) (PEI),poly(dimethyldiallylammonium chloride) (PDAC),poly(acrylamide-co-diallyl-dimethylammonium chloride)(polyquaternium-7), poly(allylamine hydrochloride) (PAH), Chitosan,polylysine, and mixtures thereof.

The second cationic polymer may also be a copolymer of non-ionic andionic monomers such as pyrrolidone/dimethylaminoethyl methacylatecopolymer.

According to another preferred embodiment of the present invention thesecond cationic additive is selected from colloidal alumina, colloidalceria (CeO2), colloidal alumina coated silica (such as Ludox CL,Sigma-Aldrich), and mixtures thereof.

The second cationic additive may be a colloidal metal oxide bearing apositive charge such as described above (e.g. colloidal alumina,colloidal ceria (CeO2), colloidal alumina coated silica, or mixturesthereof).

The non-ionic additive used in the process is preferably a non-ionicpolymer. The non-ionic polymer may be for example polyvinylalcohol,polyvinylpyrrolidone, and mixtures thereof.

The non-ionic polymer preferably carries hydrogen bonding groups such ashydroxyl, amine groups.

Further according to a preferred embodiment of the present invention,the process further comprises drying the obtained coated particulatematter.

Still further according to a preferred embodiment of the presentinvention, the drying is by a method selected from spray drying,lyophilization, oven drying, vacuum drying, and fluidized bed.

Still further according to a preferred embodiment of the presentinvention, the drying is by a method selected from spray drying,lyophilization, oven drying, vacuum drying, and fluidized bed.

Additionally, according to a preferred embodiment of the presentinvention, the process further comprises chemically modifying thesurface of the coated particulate matter.

The surface chemical modification preferably comprises modifying themetal oxide surface with organic groups, preferably hydrophobic groups.

Preferably the process comprising attaching hydrophobic groups to thesurface of the metal oxide layer.

The purpose of attaching hydrophobic groups to the surface of the metaloxide layer is to control the water penetration rate into the particlesand consequently to control the release of the active agent from theparticles. Modifying the surface of the metal oxide layer by hydrophobicgroups enables to further control the release of the active agent fromthe particles, according to the desired rate.

The hydrophobic groups may be for example an alkyl silane, dialkylsilane, trialkyl silane, (such alkyl groups may be further substitutedwith one or more fluoro atoms), aryl silane (such as benzyl silane, orphenyl silane), diaryl silane, or triaryl silane.

Moreover according to a preferred embodiment of the present invention,the chemical surface modification comprises reacting silanol groups onthe surface of the metal oxide layer with precursors selected frommonohalotrialkyl silane such as chlorotrimethylsilane, dihalodialkylsilane such as dichlorodimethyl silane, trihaloalkyl silane such astrichloromethylsilane, monoalkoxytrialkyl silane such as methoxy trimethyl silane, dialkoxydialkyl silane such as dimethoxydimethylsilane,trialkoxyalkyl silane such as trimethoxymethylsilane, aryltrihalosilanesuch as phenyltrichlorosilane, diaryldihalosilane such asdiphenyldichlorosilane, triarylhalosilane such as triphenylchlorosilane,aryltrialkoxysilane such as phenyltrimethoxysilane, diaryldialkoxysilanesuch as diphenyldimethoxysilane, triarylalkoxysilane such astriphenylmethoxysilane, and mixtures thereof.

Preferably the alkyl group includes 1-18 carbon atoms, more preferably1-6 carbon atoms. Most preferably the alkyl is methyl. The alkyl groupsmay be substituted by one or more fluoro atoms. Preferably the alkoxygroup includes 1-6 carbon atoms and more preferably 1-2 carbon atoms.

The halo group may be for example chloro, bromo, iodo, fluoro. Mostpreferably the halo groups are chloro and bromo.

The aryl is preferably phenyl or benzyl.

The precursors react with the silanol groups on the surface of the metaloxide layer to form a siloxane bond.

The attachment of the hydrophobic groups to the surface of the metaloxide layer can be performed by reacting the dried coated particulatematter with the above precursors. The procedure for attachinghydrophobic groups to the metal can be conducted as follows: a driedpowder of coated particulate matter is suspended in an organic solventsuch as toluene. A precursor (hydrophobization reagent) from the listabove such as dimethyldichlorosilane is added to the organic phase(mixture), optionally in the presence of a halogen scavenger such astrialkyl amine or triethanol amine. The organic mixture is refluxed forat least about 24 hours to obtain coverage of the metal oxide layer withthe hydrophobic groups via attachment of the hydrophobic groups to thesilanol groups on the surface of the metal oxide layer.

According to certain embodiments the particles (first and/or secondmicroparticles of the invention) may be characterized in that whentested in a Dissolution Tester using Paddle Method in a medium,typically an organic-based solvent such as acetonitrile, isopropylmiristate, ethanol or methanol, in which said particulate matter issoluble, and a dissolution volume in which the concentration of theparticulate matter is lower than the solubility of the particulatematter, the time for releasing 50% w/w of the particulate matter fromsaid particles is at least two-fold higher, preferably at leastthree-fold higher, preferably at least four-fold higher, more preferablyat least five-fold higher and most preferably at least ten-fold higheras compared to the dissolution of the free form of the particulatematter having substantially the same particle size diameter as theparticulate matter in said particles.

The dissolution of the free form of the particulate matter is measuredunder the same conditions as the coated particulate matter. The time forreleasing 50% w/w of the particulate matter (active agent) from theparticles is compared to the time of 50% w/w dissolution of the freeform. Preferably the dissolution volume is such that the concentrationof the particulate matter is lower than at least half of the solubilityof the particulate matter. The “solubility” relates to the solubility ofthe particulate matter (active ingredient) in the dissolution medium(e.g. an organic-based solvent such as acetonitrile, isopropylmiristate, ethanol or methanol). It is appreciated that the dissolutionvolume will also depend on the detection level of the analytical method.The dissolution may be conducted at a temperature of 20 C-40 C (20°C.-40° C.). The dissolution may be conducted at a paddle rate of 50-200rpm.

According to a specific embodiment the dissolution of the particles areas described above, when the particles are prepared by the repetitivecoatings steps as described in the process above.

According to certain embodiments the metal oxide layer is substantiallynot in an amorphous and/or not in a crystalline form. The term “saidmetal oxide layer is substantially not in an amorphous and/or not in acrystalline form” is meant to denote that distinct regions of amorphousmetal oxide (in case the metal oxide in its pure form is amorphous) orcrystalline metal oxide (in case the metal oxide in its pure formcontains crystalline material, or is purely crystalline) cannot bedetected by methods such as X-Ray diffraction. The non-amorphous and/ornon-crystalline metal oxide layer refers to a co-structured composite ofmetal oxide and an adhering additive. Such adhering additive may be forexample a polymer which interrupts the formation of continues regions ofthe metal oxide, thereby leading to the non-amorphous and noncrystalline metal oxide form. The non amorphous and non crystallinemetal oxide form is characterized by not having any X-ray diffractionpeak specific to the metal oxide in its pure form. For example if themetal oxide in its pure form is amorphous, a characteristic X-raydiffraction peak or peaks may be detected. This may be the case, forexample, in case of a particle with a pure metal oxide coating. In thecase of the particles according to this aspect of the invention, thecharacteristic X-ray diffraction peak(s), specific to the amorphous formis absent, shifted, or flattened. An example are particles with asilica-based coating, which will have a different peak—namely absent,shifted, or flattened—as compared to particles with an amorphous silicacoating. In the case of a metal oxide which in its pure form containscrystalline regions, or is purely crystalline, in the case of acomposite coating a peak specific to the crystalline form is absent,shifted, or flattened. Thus, X-ray diffraction may serve to distinguishparticles of this aspect of the invention over others.

According to a specific embodiment the metal oxide layer of theparticles has the characteristics as described above, when the particlesare prepared by the repetitive coating steps as described in the processabove.

The first microparticles may also be prepared by a process as disclosedin co-owned PCT application, publication number WO 2007/015243, thecontent of which is incorporated herein by reference and which isdescribed briefly below:

A process for coating a solid, water-insoluble particulate matter, witha metal oxide comprising:

(a) contacting the solid, water-insoluble particulate matter, with acationic additive in an aqueous medium to obtain a dispersion of saidparticulate matter having a positive zeta potential;

(b) coating the solid, water-insoluble particulate matter, byprecipitation of a metal oxide salt onto the surface of the particulatematter, forming a metal oxide layer thereon; and

(c) aging said coating layer.

The process may comprise subjecting the coated particulate matter to oneor more steps of precipitation of metal oxide salt, followed by agingtreatment.

In order to obtain a more robust coating, the particles obtained by theabove process (following step (c)) may be subject to further, optional,processing steps to cause precipitation of more metal oxide on theinitially formed metal oxide layer. Such further processing may includealso an aging step, similar to step (c). Additionally, the precipitationstep of the additional processing may also involve a step, similar tostep (a) above, in which a positive zeta potential is formed on thecoating layer (i.e. the metal oxide coating layer), through the additionof a cationic additive, which may be the same or may be different tothose used in said step (a). The further processing step may be repeatedone, two, three or a plurality of more times.

step (c) may further comprise after aging, separating the coatedparticulate matter from the dispersing aqueous medium and optionallyrinsing and redispersing the obtained coated particulate matter in anaqueous medium.

step (c) may further comprise after redispersing the coated particulatematter in an aqueous medium, adding a second cationic additive to obtaina positive zeta potential of the coating layer.

Alternatively, the further processing steps may be conducted without theaddition of a cationic additive. In such a case, the process preferablycomprises:

(a) contacting the solid, water-insoluble particulate matter, with afirst cationic additive in an aqueous medium to obtain a dispersion ofsaid particulate matter having a positive zeta potential;

(b) coating the solid, water-insoluble particulate matter, byprecipitation of a metal oxide salt onto the surface of the particulatematter, forming a metal oxide layer thereon;

(c) aging said coating layer to obtain first coated particulate matter;

(d) coating the first coated particulate matter by precipitation of ametal oxide salt onto the surface of the particulate matter, forming ametal oxide layer thereon; and

(e) aging said coating layer to obtain second coated particulate matter;

The process may further comprise:

(f) coating the second coated particulate matter by precipitation of ametal oxide salt onto the surface of the particulate matter, forming ametal oxide layer thereon; and

(g) aging said coating layer to obtain third coated particulate matter.

In the absence of a cationic additive in the further processing stepsthe positive zeta potential in step (a) is preferably less than +150 mV,and more preferably in the range +60 mV to +130 mV. The zeta potentialof the coated particulate matter after aging may be in the range 0 mV to−60 mV.

In order to ensure the deposition of further metal oxide layers in thefurther processing steps by electrostatic interaction and also tocontrol the thickness of the metal oxide (e.g. silica) layers it ispreferable to use a second cationic additive.

Preferably the process comprises:

(a) contacting the solid, water-insoluble particulate matter, with afirst cationic additive in an aqueous medium to obtain a dispersion ofsaid particulate matter having a positive zeta potential;

(b) coating the solid, water-insoluble particulate matter, byprecipitation of a metal oxide salt onto the surface of the particulatematter, forming a metal oxide layer thereon;

(c) aging said coating layer to obtain first coated particulate matter;

(d) contacting the first coated particulate matter with a secondcationic additive in an aqueous medium to obtain a dispersion of saidfirst coated particulate matter having a positive zeta potential andfurther processing the dispersion through steps (b) and (c) to obtain afurther processed, coated particulate matter.

The process may further comprise, processing the coated particulatematter obtained in (d) through another step (d).

Preferably the coated particulate matter and the second cationicadditive are mixed, and most preferable said mixing is under vigorousstirring (e.g. mixer speed above 1000 rpm).

The first cationic additive used in step (a) of the process has a dualeffect: to increase the zeta potential of the particulate matter as willbe described below, and also to serve as a wetting agent, thus allowingdispersion of the particulate matter as discrete core particles, whereeach core particle is individually suspended in the aqueous medium.

It is important that the surface of the particulate matter be reactiveor be made subject to bonding with metal oxide layer.

The purpose of step (a) is to modify the zeta potential of theparticulate matter by using a cationic additive such that it will bemade reactive to the attachment of the metal oxide layer.

For preparing the core material of the particles, the particulate matterought to be suitably coated with a first cationic additive, such that itcan be attached to the precipitated metal oxide salt. The particulatematter is contacted with a first cationic additive, for example bymixing it with a solution of a cationic surfactant or cationic polymer.Cationic surfactants are particularly effective in being adsorbed uponthe surface of the particulate matter and they need to be used insufficient amount to provide a positive zeta potential of theparticulate matter (preferably in the range above 0 mV and up to +150mV, more preferably +60 mV to +130 mV).

A monolayer of the cationic additive is preferred, but the coating neednot be continues. It is sufficient that there are at least spots ofcationic additive. These spots will then serve as anchors for theattachment of the metal oxide layer. It is preferred that there arefairly uniform distribution of these anchoring points on the coresurface so that as the metal oxide layer builds up it will bridge overand be firmly attached to the core.

Preferably the process comprising repeating step (d) one or twoadditional times, most preferably one additional time.

The first and second cationic additive may be the same or different.

Most preferably the first cationic additive is a surfactant and thesecond cationic additive is a cationic polymer.

Step (c) may further comprise after aging, separating the coatedparticulate matter from the dispersing aqueous medium and optionallyrinsing and redispersing the obtained coated active ingredient in anaqueous medium.

Preferably the separation of the coated particulate matter is conductedby a method such as filtration centrifugation, dialysis, or byevaporation of the aqueous medium.

Step (b) may comprise contacting said dispersion obtained in (a) with ametal oxide salt under conditions so as to precipitate the metal oxidesalt onto surface of the particulate matter, yielding a coating layerthereon.

Step (b) may comprises adding a metal oxide salt to yield a value of pH7-11; and acidifying to yield a pH value of 1-3 (more preferably a pH ofabout 2).

More preferably step (b) comprises adding a metal oxide salt to reach avalue of 8-10; and acidifying to obtain a value of 1-3 (more preferablya pH of about 2).

When the particulate matter is an acidic compound it may be preferred toadd a metal oxide salt to reach a pH value of 7-8; and acidifying toobtain a value of 1-3.

Step (b) may further comprise adjusting the pH of the dispersionobtained in (a) to a value in the range 5.5-8 before adding a metaloxide salt, more preferably to a pH value in the range 7-8 before addinga metal oxide salt.

The purpose of the pH adjustment of the dispersion to a value between5.5-8 is to form negatively charged metal oxide species that will bebound to the positively charged particulate matter surface thus enablingthe attachment of the metal oxide layer on the surface of theparticulate matter.

Preferably step (b) is repeated at least 1-3 additional times (i.e. one,two or three more times). Most preferably step (b) is repeated oneadditional time.

The positive zeta potential in step (a) is preferably less than +150 mV(+150 or less, i.e. above 0 and up to +150 mV), and more preferably inthe range +60 mV to +130 mV).

Preferably the positive zeta potential in step (d) is less than +150 mV(+150 or less, i.e. above 0 and up to +150 mV), more preferably in therange +5 mV to +130 mV, and most preferably +10 to +100 mV.

The aging in step (c) is crucial for obtaining a strengthened and denselayer of metal oxide.

Preferably step (c) comprises raising the pH to a value in the range6.5-9.5, preferably to a range of 7.5-8.5, and mixing, e.g. by stirring,the suspension (dispersion) in this pH range for a period of at least 12h (twelve hours). Preferably stirring is for 12-72 h, more preferably atleast 20 h (for example 20-72 h), even more preferably for 36 h-72 h,and most preferably for 40-50 h.

The stirring is preferably a gentle stirring, preferably in the range200-500 rpm.

An indication for the completion of aging can be obtained by constantzeta potential measurements upon repeated increased dilutions. Further,upon completion of aging, the filtration will be easy to perform (due tothe hard metal oxide layer formed) and the obtained cake will be easilyredispersed in an aqueous medium to form a dispersion of particles.

The purpose of aging in step (c) is to obtain a strengthened and denserlayer of metal oxide and therefore to enable the growth of the metaloxide layer on the core material.

The aging may be conducted at a temp of 4-90° C., preferably at 15-60°C. and most preferably the aging is conducted at a temperature 20°C.-40° C.

Thus the repeated steps of coating and aging also enable the growth ofthicker and stronger layer of metal oxide.

Preferably the positive zeta potential in step (a) is less than +150 mV,more preferably zeta potential in the range +60 mV to +130 mV. Thepreferred zeta potential in step (d) is less than +150 mV, morepreferably in the range +5 mV to +130 mV, and most preferably +10 mV to+100 mV. This is the preferred zeta potential also in the further,optional, processing steps.

The metal oxide salt may be as described above.

The cationic additive (i.e. first and/or second cationic additive) maybe a cationic surfactant, a cationic polymer, and mixtures thereof. Mostpreferably the first cationic additive is a cationic surfactant, and thesecond cationic additive is a cationic polymer.

The first cationic additive is preferably a cationic surfactant.

The cationic surfactant may be monoalkylquaternary ammonium salts,dialkyl quaternary ammonium salts, and mixtures thereof.

The monoalkylquaternary ammonium salts may be benzethonium chloride,benzalkonium chloride, cetyltrimethylammonium chloride (CTAC),cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium chloride,stearyltrimethylammonium chloride, cetylpyridinium chloride, andmixtures thereof.

Most preferably the monoalkylquaternary ammonium salt iscetyltrimethylammonium chloride.

Preferably the dialkyl quaternary ammonium compound isdistearyldimethylammonium chloride.

Additional cationic surfactants which can be used are described in: JohnA. Wenninger et al. (Editors) International Cosmetic IngredientDictionary and Handbook (Eighth Edition 2000), Vol. 2 pp. 1140-1147,Published by The cosmetic, Toiletry, and Fragnance Association,incorporated herein by reference in its entirety.

Preferably the weight ratio of the first cationic additive to thewater-insoluble particulate matter is in the range 1:1000-1:10, morepreferably 1:200-1:50, most preferably about 1:100.

The second cationic additive may be a cationic polymer, a cationicsurfactant or mixtures thereof. The cationic surfactant may be asdescribed above.

Preferably the second cationic additive is a cationic polymer.

Preferably the weight ratio of the second cationic additive to the firstcoated particulate matter is in the range 1:1000-1:10, more preferably1:200-1:50, most preferably about 1:100.

Preferably the weight ratio of the second cationic additive to thefurther processed coated particulate matter (e.g. second coatedparticulate matter) is in the range 1:1000-1:10, more preferably1:200-1:50, most preferably about 1:100.

Preferably the cationic polymer (of the first cationic additive orsecond cationic additive) is selected from poly(ethyleneimine) (PEI),poly(dimethyldiallylammonium chloride) (PDAC),poly(acrylamide-co-diallyl-dimethylammonium chloride)(polyquaternium-7), poly(allylamine hydrochloride) (PAH), Chitosan,polylysine, and mixtures thereof.

The second cationic additive may be for example colloidal alumina,colloidal ceria (CeO2), colloidal alumina coated silica (such as LudoxCL, Sigma-Aldrich), and mixtures thereof.

The second cationic additive may be for example a colloidal metal oxidebearing a positive charge such as described above (e.g. colloidalalumina, colloidal ceria (CeO2), colloidal alumina coated silica, ormixtures thereof).

The process may further comprise drying the obtained coated particulatematter.

The drying may be conducted by a method selected from spray drying,lyophilization, oven drying, vacuum drying, and fluidized bed.

The first microparticles may also prepared by spray drying as describedfor example in:

-   Iskandar, F. et al, Preparation of microencapsulated powders by an    aerosol spray method and their optical properties, Advanced Powder    Technol., 14(3):349-367, 2003;-   Iskandar, F. et al, Control of the morphology of nanostructured    particles prepared by the spray drying of a nanoparticle sol,    Journal of Colloid and Interface Science, 265:296-303, 2003;-   Kortesue, P. et al, In vitro evaluation of sol-gel processed spray    dried silica gel microspheres as carrier in controlled drug    delivery, International Journal of Pharmaceutics, 200:223-229, 2003;-   Takeuchi, H. et al, Solid dispersion particles of tolbutamide    prepared with fine silica particles by the spray-drying method,    Powder Technology, 141:187-195, 2004;-   Kortesuo, P. et al, Biomaterials, 23:2795-2801, 2002;-   incorporated herein by reference in their entirety.

The second microparticles may also be prepared in the same manner, bythe methods described above for the first microparticles.

The peroxide (e.g. BPO) and retinoid (e.g. tritenoin (ATRA)) combinationin the same composition can be designed to have differentiation in therelease profile of the active agents by modification of the metal oxide(e.g. silica) layer formed on each active agent. Microparticlescomprising BPO for example can have a thick silica layer thus providinga slow release profile while microparticles comprising ATRA can have athin silica layer or the ATRA can have no coating layer at all, thusproviding a fast release profile.

The invention additionally relates to a composition for topicalapplication as defined in the present invention the composition havingreduced side affects as compared to a reference composition in which theactive ingredients are uncoated.

According to a preferred embodiment of the present invention the sideeffects are selected from irritation, erythema, stringing, itching,scaling, dryness, and combinations thereof.

The side effects may also be other similar dermal undesirable sideeffect.

The invention further relates to a method for treating a surfacecondition in a subject comprising topically administering onto thesurface a composition as described in the present invention.

Preferably the surface is skin or mucosal membrane. Preferably thesurface condition is selected from acne, rosecea, psoreasis, photoagingskin, hyperpigmented skin, mucosal infected areas, inflamed dermatitis,and combinations thereof.

Such surface conditions are preferably treatable by retinoids andperoxides.

Preferably the subject is a mammal and most preferably the mammal is ahuman.

The term “treating or treatment” as used herein includes any treatmentof a condition (disease or disorder such as acne, rosecea, psoreasis,and combinations thereof) associated with a patient's body surface suchas the skin or mucosal membrane and includes inhibiting the disease ordisorder (i.e. arresting its development), relieving the disease ordisorder (i.e. causing regression of the disease or disorder) orrelieving the conditions caused by the disease (i.e. symptoms of thedisease).

The concentrations of the active ingredients that can be used fortreatment of a specific disease or disorder may be 1%-20% w/w BPO and0.005%-0.5% w/w ATRA, preferably 2.5%-15% w/w BPO and 0.01%-0.2% w/wATRA, most preferably 2.5%-10% w/w BPO and 0.025%-0.1% w/w ATRA, basedon the total weight of the composition. Although individual needs mayvary, determination of optimal ranges for effective amounts of thecomposition is within the skill of the art. Generally, the dosagerequired to provide an effective amount of a composition which can beadjusted by one skilled in the art will vary depending on the age,health, physical condition, weight, type and extent of the disease ordisorder of the recipient, frequency of treatment, the nature ofconcurrent therapy, if any, and the nature and scope of the desiredeffect.

Moreover, the present invention relates to a method for preparing acomposition comprising as active ingredients a peroxide and a retinoidwhich are chemically unstable when formulated together, wherein thecomposition exhibits improved stability of at least one of the activeingredients, the method comprising:

(a) separating said peroxide and retinoid from each other in thecomposition by coating a solid particulate matter of one of said activeingredients by a metal oxide coating layer to form first microparticles,the other of said peroxide and retinoid is incorporated into thecomposition in an uncoated free form or in a coated form of the activeingredient; and

(b) adding excipients for the preparation of the composition.

As used herein the term “chemical unstable” refers to active ingredientswhich degrade, decomposes, chemically reacts one with the otherresulting in a decrease of the active ingredient initial concentration.The term “chemical unstable” encompasses also “photochemical instablity”as a result of light irradiation. Preferably the improved stabilityrefers to the retinoid.

As used herein by the term “separating” is meant that above 90% w/w,preferably above 95% w/w and more preferably above 99% w/w of the totalinitial amount of the peroxide present in the composition and above 90%w/w, preferably above 95% w/w and more preferably above 99% w/w of thetotal initial amount of the retinoid present in the composition areseparated (i.e. not in direct contact or not intimately mixed) from eachother in the same composition.

Preferably, the coated form of the active ingredient is prepared bycoating a solid particulate matter of the active ingredient by a metaloxide coating layer to form second microparticles. Preferably thecoating is as described in the present invention.

The present invention further relates to a kit comprising: (a) a firstcomposition comprising a peroxide as a first active ingredient; and (b)a second composition comprising a retinoid as a second activeingredient; at least one of said first and said second active ingredientbeing coated by a metal oxide layer.

Preferably one of the first and the second active ingredient beingcoated by a metal oxide layer and the other is present in an uncoatedfree form or in a coated form of the active ingredient.

According to a preferred embodiment the kit further comprisinginstructions for use in the treatment of a disease or disorder selectedfrom one or more of acne, rosacea, psoriasis, photoaging skin,hyperpigmented skin, inflamed dermatitis, mucosal infected areas, theuse comprising combining said first and said second composition for saidtreatment.

The present invention additionally relates to a method of using the kitas described in the present invention wherein said first composition andsaid second composition are applied concomitantly or sequentially (onesubsequent to the other) onto a surface of a subject's body.

EXAMPLES

In the examples below, all % values referring to a solution are in(w/w).

All % values, referring to dispersions (suspensions) are in (w/w).

Unless otherwise indicated, all solutions used in the example belowrefer to an aqueous solution of the indicated ingredient.

Example #1 Silica Encapsulation (Coating) of BPO

Step 1: milling: 110 g. of hydrous BPO 75% (USP grade from Sigma, USA)were suspended in 152 g. of 0.4% CTAC solution containing 0.001% siliconantifoam. The BPO was milled using a stator rotor mixer (IKA 6100operated at 15,000 rpm). The milling was stopped when the particle sizedistribution (PSD) of the suspension was d(0.9)≦35 μm or the temperaturehas reached 50 C. The final suspension was cooled to room temperature.

Step 2: coating: During the coating procedure the suspension was stirredwith a mechanical dissolver, 60 mm, at 500 RPM at all times. The pH ofthe milled BPO suspension was corrected to 8 using NaOH 5N solution. Aportion of 1 g of 15% sodium silicate solution (15% w/w as SiO₂) wasadded and the suspension was stirred for 5 min. A portion of 1 g of 3%Polyquaternium 7 (Poly diallyl ammonium chloride) was added and thesuspension was stirred for 5 min. pH was adjusted to 6-7 using 5N HClsolution.

This procedure was repeated for 5-100 times in order to create a seriesof silica layers around BPO having different thicknesses.

The aging step: The coated BPO suspension at pH 6.5 was kept for agingat room temperature under gentle agitation for 24 hrs.

Example #2 Analytical Evaluation of the BPO Release

The release profile of BPO out of the silica shell was conducted in awater/Acetonitrile solution, which is capable of dissolving BPO. Themethod is based on the strong oxidation properties of BPO. BPO reactswith I⁻ ions to form I₂, which gives a color reaction. I₂ is thenreduced back to I⁻ using sodium thiosulfate (STS) to eliminate thecolor. Each 12.11 mg of oxidizing BPO can be reduced by 1 ml of 0.1MSTS. The evaluation of BPO release was conducted using Solution A andSuspension B as detailed below

Composition of 100 g. solution A, (capable to distinguish release of 30%BPO): 55 g. Acetonitrile, 12.4 g. 0.1M STS, 4.5 g. KI, 28.1 g. deionizedwater. Suspension B, preparation of BPO: weigh 200 mg of BPO as 100% (1g as 20% BPO suspension into 5 ml measuring bottle and fill withdeionized water up to 5 ml. Procedure: Into 50 ml glass beaker add 40 mlof solution A and the 5 ml of suspension B. Measure the time for yellowcolor appearance.

Results:

Time for color Sample Number of coating cycles appearance (min)Brevoxyl ™ 8%^((a)) Commercial product 3 NeoBenz ™ 5.5%^((b)) Commercialproduct 8 SGT-V5, 20%^((c)) 5 16 SGT-V10, 20%^((c)) 10 37 SGT-V15,20%^((c)) 15 108 SGT-V20, 20%^((c)) 20 152 ^((a))Commercial productcontaining 8% w/w BPO. ^((b))Commercial product containing 5.5% w/w BPO.^((c))Containing 20% w/w BPO in the suspension. All are normalized to200 mg BPO in the test method.

Example #3 Silica Encapsulation of Tretinoin

LUDOX TM-50 (purchased from Sigma, USA) is a nanometric suspension ofsilica (5-20 nm) at pH 9.0. The pH of the Ludox suspension was adjustedto 5-6 using 5N HCl solution. Different amounts of all trans Retinoicacid (Tretinoin) (USP grade from Rhodia) were mixed with pH adjustedLudox suspension to obtain silica/ATRA ratios of 50/50 up to 90/10respectively. The suspension was diluted to 20% solids and was milledusing a M-110Y microfluidizer processor (Microfluidics) at 15,000 psi.The milling was stopped when the particle size distribution (PSD) of thesuspension was d(0.9)≦5 μm. The temperature was kept below 30 C at alltimes. The milled suspension was spray dried by a spray drier at inlettemperature of 100 C, outlet temperature of 60 C to obtain silicaspheres entrapping tretinoin particles.

Example #4 Analytical Evaluation of the ATRA Release

The release profile of ATRA (Tritinoin) out of the silica shell was donein a water/THF solution at pH=3, which is capable of dissolving ATRA.The amount of released ATRA was measured by titration. All samplescontained 0.1 w/w Tritinoin.

Results:

Time for titration of Sample Silica/ATRA ratio 30% ARTA (min) Retin A ™0.1% Commercial product 5 Retin A Micro ™ 0.1% Commercial product 13SGT-T50, 0.1% 50/50 24 SGT-T30, 0.1% 70/30 40 SGT-T10, 0.1% 90/10 57

Example #5 Stability Study of BPO/ATRA Mixture

A water based gel formulation containing 5% BPO and 0.1% ATRA wasprepared using free and encapsulated active agents. The followingmixtures were prepared using samples from examples 2 and 4:

Sample # BPO ATRA A Non-encapsulated Non-encapsulated B SGT-V20Non-encapsulated C SGT-V20 SGT-T50 D SGT-V5 SGT-T10 E SGT-V20 SGT-T10 FNon-encapsulated SGT-T10

The gels were placed for stability at the following temperatures: 4 C,25 C and 30 C and the degradation in ATRA concentration was measured.

Results:

Degradation of ATRA as % from initial concentration Sample 4 C. 25 C. 30C. # 1* 2 3 1 2 3 1 2 3 A 13.1 33.9 59.1 83.5 100 — 100 — — B 0.5 0.81.2 4.5 8.8 17.3 29.5 100 — C 0.3 0.5 0.9 2.8 7.1 12.4 27.3 100 — D 0.61.1 1.9 6.2 13.9 27.1 55.3 100 — E 0.1 0.1 0.3 1.8 3.4 6.9 9.1 20.5 54.3F 2.3 4.9 9.7 31.8 78.3 100 65.1 100 — *Time in months

It is clearly shown that the encapsulation of the APIs (activepharmaceutical ingredients) increases dramatically the stability ofATRA. The most stable combination is mixture E in which both BPO andATRA have the longest release time. The encapsulation of BPO is moresignificant to the stability than that of ATRA.

Example #6 In-House Irritation Patch Test

The water based gel formulations from example #5 were tested in a 4 hrspatch test. The compounds were applied once during the study, at time 0.Removal of the patches was after 4 hrs. Observation and pictures of theapplication areas (FIG. 1) were taken after additional 24 hrs (total 28hrs).

The picture shows the irritation caused by samples A, B, C and E. Thestrong irritation of the non-encapsulated sample (A) is clearly shown.Sample B has much lower irritation whereas samples C and E arecompletely non-irritant.

Example #7 Silica Encapsulation of Tretinoin

Step 1: milling: 75 g. of all trans Retinoic acid (Tretinoin) (USP gradefrom Rhodia) were suspended in 250 g. of 0.3% CTAC solution containing0.001% silicon antifoam. The ATRA was milled using a M-110Ymicrofluidizer processor (Microfluidics) at 15,000 psi. The milling wasstopped when the particle size distribution (PSD) of the suspension wasd(0.9)≦20 μm. The temperature has kept below 30 C at all times.

Step 2 coating: During the coating procedure the suspension was stirredwith a mechanical dissolver, 60 mm, at 500 RPM at all times. The pH ofthe milled ATRA suspension was corrected to about 4 using HCl 5Nsolution. A portion of 0.5 g of 15% sodium silicate solution (15% w/w asSiO₂) was added and the suspension was stirred for 5 min. A portion of0.5 g of 3% Polyquaternium 7 was added and the suspension was stirredfor 5 min. pH was readjusted to about 4 using 5N HCl solution. Thisprocedure was repeated for 5-100 times in order to create a series ofsilica layers around ATRA having different thicknesses.

The aging step: The coated ATRA suspension at pH 4.5 was kept for agingat room temperature under gentle agitation for 24 hrs.

Example #8 Silica Encapsulation of Tazarotene (TAZ)

Step 1: milling: 50 g. of Tazarotene (from Glenmark) were suspended in350 g. of 0.3% CTAC solution containing 0.001% silicon antifoam. The TAZwas milled using a M-110Y microfluidizer processor (Microfluidics) at15,000 psi. The milling was stopped when the particle size distribution(PSD) of the suspension was d(0.9)≦25 μm. The temperature was kept below30 C at all times.

Step 2: coating: During the coating procedure the suspension was stirredwith a mechanical dissolver, 60 mm, at 500 RPM at all times. The pH ofthe milled TAZ suspension was corrected to about 3 using HCl 5Nsolution. A portion of 1 g of 15% sodium silicate solution (15% w/w asSiO₂) was added and the suspension was stirred for 5 min. A portion of0.3 g of 3% Polyquaternium-1 was added and the suspension was stirredfor 5 min. pH was readjusted to about 3 using 5N HCl solution.

This procedure was repeated for 50 times in order to create silicalayers around TAZ.

The aging step: The coated TAZ suspension at pH 4.5 was kept for agingat room temperature under gentle agitation for 24 hrs.

Example #9 Tretinoin Stability Test 1.0 Method Objective and Principle

The ATRA (All-trans-Retinoic acid) was tested for stability in presenceof Benzoyl peroxide (BPO) at a ratio of 0.1% ATRA to 6% BPO. Thestability screening was performed in water: ATRA and BPO werere-suspended in water for 4 hours at 40° C. (testing time zero and 4hours, or other). At the end of the procedure the ATRA was extractedwith dilution solution containing BHT (for better stability of samplepreparation) and determined using HPLC method against external standardat 352 nm.

2.0 Reagents and Equipments

Acetonitrile HPLC grade Water HPLC grade Isopropyl alcohol (IPA) HPLCgrade Glacial acetic acid HPLC grade Butylated hydroxytoluene (BHT)Analytical grade Column Zorbax RX-C18 3.5 μm 4.6 * 150 mm Eluent 70%Acetonitrile and 30% of 1% Acetic acid in Water Flow rate 1.3 ml/min.Detection UV, Wavelength 352 nm. Injection Volume 10 μL ColumnTemperature 40° C.

2.1 Dilution Solution Preparation

Dissolve 1 g of BHT in 1000 ml of Acetonitrile.

3.0 ATRA Standard Preparation

Weight approximately 50 mg of ATRA RS into a 50 ml low actinicvolumetric flask add about 30 ml of IPA. Sonicate for 10 min, cool toroom temperature and fill to volume (Stock solution). Transfer 2 ml ofstock solution to a 50 ml low actinic volumetric flask, fill to volumewith dilution solution (solution S).

4.0 System Suitability Solution

See ATRA Standard Preparation.

5.0 Sample Preparation

Fill a 3 ml Pasteur pipette with sample. Transfer the pipette content toa previously weighed 50 ml volumetric flask. Weigh the flask, add 30 mlof dilution solution, and sonicate for 15 minutes (avoid heating). Fillto volume with dilution solution, and filter through 0.2μ Nylon SyringeFilter, discard the first ml (solution A).

6.0 Procedure

Samples and standards should be prepared in duplicates.

Sample and Standard Preparation should be prepared and sampled at thesame temperature.

7.0 Calculation

Calculate the ATRA assay in the sample using the formula:

${\% \mspace{14mu} {ATRA}} = \frac{{Asample}*{Cstd}*\% \mspace{14mu} {Pstd}}{{Astd}*{Csample}}$

Where:

Asample—ATRA peak area arising from the Sample Preparation.Astd—ATRA peak area arising from the Standard Preparation.Csample—Sample Concentration in mg/ml.Cstd—Standard Concentration in mg/ml.% Pstd—% Purity of the standard

Example #10 Coating Using Sodium Silicate and a Polymer

Tretinoin crystals were encapsulated with several cycles of sodiumsilicate and either PVA (polyvinyl alcohol) or PDAC-7(polyquaternium-7). The cycles each consisted of the following steps:first, sodium silicate was added until the pH reached 7; the solutionwas then acidified with HCl (usually 1 M solution) to pH 3, at whichpoint the polycation or non-ionic polymer was added. After the lastcycle, a final layer of sodium silicate and HCl was applied. On severaloccasions, Ludox TM 50 (Grace davision, USA) (2.5%) was added to thesodium silicate solution for the coating. BHT (butylated hydroxytuluene)was added in some cases to the tretinoin before the milling process asan anti-oxidant. 5% tretinoin in water containing 0.3% CTAC was used inall cases was milled in a microfluidizer (d (0,9)≦12-13 μm). Stabilityof the encapsulated tretinoin crystals was checked with a BPO solutionas described in example #9.

Results

An assortment of coatings on the tretinoin crystals was performed. Atfirst we compared the degradation of the tretinoin when coated with 10cycles of sodium silicate (2.5%) and PDAC-7 with and without BHT. It wasfound that the addition of BHT prevented the degradation of tretinoin by15-20% (FIG. 2). Therefore, all further experiments were conducted withthe addition of BHT.

In order to obtain better stability with BPO, we compared two polymers:PDAC-7 and PVA. Generally the PDAC-7 gave slightly better stabilityresults.

The results show that the more coating cycles performed, the better thestability of the active ingredients. For example, the comparison between15 to 30 cycles shows that when increasing the number of cycles, thestability grows.

The addition of Ludox (TM-50) to the sodium silicate solution to give a2.5% w/w solution of S.S. (Sodium Silicate) and 2.5% w/w Ludox, each,usually resulted with better stability. Without being bound to theory,this is perhaps the result of the fact that the Ludox supplies partiallyformed silica to the shell, which does not always form completely whenonly sodium silicate is used. This can be seen in FIG. 3.

Conclusions

It is evident from the results that were obtained that in order toachieve better stability the number of coating cycles should beincreased.

TABLE 1 Summary of the stability experiments. % Degradation as measuredby Sample BHT # Of cycles Ludox Polymer Remarks example #9^((a))11303002 − 10 − PDAC 33.1 11303502 + 10 − PDAC 15.7 11304402 − 5 − PVA78.1 11304502 − 10 − PVA 62.6 11304702 + 10 − PVA 42.8 11305202 + 15 −PVA 69.2 11306002 + 10 + PVA 56.1 11306202 + 10 − PDAC 42.8 11306402 +10 − PDAC 57.7 11306902 + 30 + PVA 40.7 11307002 + 50 + PVA 24.211307102 + 10 + PDAC 56.1 11307502 + 15 + PDAC 58.7 11307503 + 30 + PDAC11307502 filtered 37.9 and then repeated ^((a))after four hours at 40°C. at pH 5.The results are also shown in FIG. 4.

Method of Determining Coated Tretinoin Release Profile (Assay Method(#03/1-AS-01)) Method Principle

To evaluate the release of ATRA (All-trans-Retinoic acid) fromencapsulated product. The encapsulated ATRA product was extracted by abiphasic extraction system, by re-suspending ATRA product in abuffer/IPM (isopropylmeristate) at room temperature and tested at timezero and every few hours, or other. At the end of the procedure the ATRAwas determined by HPLC method against external standard at 352 nm.

The reagents, equipments, standard and sample preparations, andanalytical procedures used are detailed in example #9.

Sample Preparation

Transfer a quantity of encapsulated ATRA product, equivalent to about 20mg of ATRA, to a 250 ml amber Erlenmayer flask. Add 100 ml of phosphatebuffer, mix. Add 100 ml of IPM and stir on a magnetic stirring plate at500 rpm. Remove 1.0 ml of upper layer at different time intervals intoeppendorf. Centrifuge for 1 minutes at 10000 rpm. Transfer 0.5 ml ofclear liquid into 25 ml amber volumetric flask, dilute to volume withAcetonitrile and filter through 0.2μ Nylon Syringe Filter, discard thefirst ml (solution A).

Calculation

Calculate the % of ATRA released using the formulas:

${\% \mspace{14mu} {released}} = {\frac{\% \mspace{14mu} {ATRA}}{{Assay}\mspace{14mu} (\%)}*100}$

Where:

Assay(%)—content of ATRA in the sample according to assay method(#03/1-AS-01).

${\% \mspace{14mu} {ATRA}} = \frac{{Asample}*{Cstd}*\% \mspace{14mu} {Pstd}}{{Astd}*{Csample}}$

The parameters Asample, Cstd, % Pstd, Astd, Csample are described abovein Example #9 under “calculation”.

While this invention has been shown and described with reference topreferred embodiments thereof, it will be understood by those skilled inthe art that many alternatives, modifications and variations may be madethereto without departing from the spirit and scope of the invention.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference.

1. A composition for topical application comprising as an activeingredient a peroxide and a retinoid wherein one of said peroxide andretinoid is in the form of first microparticles comprising a solidparticulate matter of the active ingredient coated by a metal oxidelayer and the other of said peroxide and retinoid is present in anuncoated free form or in a coated form of the active ingredient.
 2. Thecomposition of claim 1, wherein said coated form of the activeingredient is second microparticles comprising a solid particulatematter of the active ingredient coated by a metal oxide layer.
 3. Thecomposition of claim 1, wherein said first microparticles comprise asolid particulate matter of a peroxide coated by a metal oxide layer. 4.The composition of claim 1, wherein said peroxide is in the form offirst microparticles comprising solid particulate matter of peroxidecoated by a metal oxide layer and said retinoid is in the form of secondmicroparticles comprising a solid particulate matter of retinoid coatedby a metal oxide layer.
 5. The composition of claim 1, wherein saidperoxide is benzoyl peroxide.
 6. The composition of claim 1, whereinsaid retinoid is selected from all trans retinoic acid, iso-tretinoin,adapalene, tazarotene, and mixtures thereof.
 7. The composition of claim1 having an improved stability as compared to a reference compositionthe difference between said composition and the reference compositionbeing in that in the reference composition the active ingredients arenot coated.
 8. The composition according to claim 1 further comprisingan additional active agent.
 9. The composition of claim 8 wherein saidadditional active agent is an antibiotic agent.
 10. The compositionaccording to claim 1, wherein said metal oxide is selected from silica,titania, alumina, zirconia, ZnO, and mixtures thereof.
 11. Thecomposition according to claim 10, wherein said metal oxide is silica.12. A composition for topical application comprising as an activeingredient benzoyl peroxide and all trans retinoic acid wherein one ofsaid benzoyl peroxide and all trans retinoic acid is in the form offirst microparticles comprising a solid particulate matter of the activeingredient coated by a metal oxide layer and the other of said benzoylperoxide and all trans retinoic acid is present in an uncoated free formor in a coated form of the active ingredient.
 13. A composition fortopical application comprising as an active ingredient benzoyl peroxideand tazarotene wherein one of said benzoyl peroxide and tazarotene is inthe form of first microparticles comprising a solid particulate matterof the active ingredient coated by a metal oxide layer and the other ofsaid benzoyl peroxide and tazarotene is present in an uncoated free formor in a coated form of the active ingredient.
 14. The composition ofclaim 1, wherein said first microparticles are prepared by deposition ofmetal oxide on the surface of the solid particulate matter.
 15. Thecomposition of claim 14 wherein said first microparticles are preparedby (a) contacting the solid, water-insoluble particulate matter, with anionic additive and an aqueous medium to obtain a dispersion of saidparticulate matter having positive charges on its surface; (b) coatingthe solid, water-insoluble particulate matter, by precipitation of ametal oxide salt onto the surface of the particulate matter, forming ametal oxide coating layer thereon; and (c) aging said coating layer. 16.A composition for topical application as defined in claim 1, saidcomposition having reduced side effects as compared to a referencecomposition in which the active ingredients are uncoated.
 17. Thecomposition of claim 16, wherein said side effects are selected fromirritation, erythema, stinging, itching, scaling, dryness, andcombinations thereof.
 18. A method for treating a surface condition in asubject comprising topically administering onto the surface acomposition of claim
 1. 19. The method of claim 18, wherein said surfaceis skin or mucosal membrane.
 20. The method of claim 18, wherein saidsurface condition is selected from acne, rosacea, psoriasis, photoagingskin, hyperpigmented skin, mucosal infected areas, inflamed dermatitis,and combinations thereof.
 21. A method for preparing a compositioncomprising as active ingredients a peroxide and a retinoid which arechemically unstable when formulated together, wherein the compositionexhibits improved stability of at least one of the active ingredients,the method comprising: (a) separating said peroxide and retinoid fromeach other in the composition by coating a solid particulate matter ofone of said active ingredients by a metal oxide coating layer to formfirst microparticles, the other of said peroxide and retinoid isincorporated into the composition in an uncoated free form or in acoated form of the active ingredient; and (b) adding excipients for thepreparation of the composition.
 22. The method of claim 21, wherein saidcoated form of the active ingredient is prepared by coating a solidparticulate matter of the active ingredient by a metal oxide coatinglayer to form second microparticles.
 23. A kit comprising: (a) a firstcomposition comprising a peroxide as a first active ingredient; and (b)a second composition comprising a retinoid as a second activeingredient; at least one of said first and said second active ingredientbeing coated by a metal oxide layer.
 24. The kit of claim 23 wherein oneof said first and said second active ingredient being coated by a metaloxide layer and the other is present in an uncoated free form or in acoated form of the active ingredient.
 25. The kit of claim 23, furthercomprising instructions for use in the treatment of a disease ordisorder selected from one or more of acne, rosacea, psoriasis,photoaging skin, hyperpigmented skin, inflamed dermatitis, mucosalinfected areas, the use comprising combining said first and said secondcomposition for said treatment.
 26. A method of using the kit of claim23 wherein said first composition and said second composition areapplied concomitantly or sequentially onto a surface of a subject'sbody.